1. Field of the Invention
The present invention relates to an apparatus for inspecting integrated circuits by applying test signals to integrated circuits as devices to be inspected (DUT).
2. Description of Related Art
Integrated circuit testers (IC testers) are conventionally used for inspecting integrated circuits. Because the conventional tester applies a phase signal (time based signal) to each pin of an integrated circuit to be inspected, it is necessary to provide the same number of signal cables as there are pins (for example, 1024 pins would require 1024 signal cables) in the vicinity of the integrated circuit.
However, because the sizes of recent integrated circuits have become smaller, it has become difficult to arrange and connect a large number of signal cables in the confined spaces around the integrated circuit. In particular, in the case where optical fibers are used so that phase signals to be applied to pins do not generate phase shifts due to line conditions such as impedance losses, it not only becomes more difficult to arrange and connect these optical fibers, but it also results in an increase in the manufacturing cost of the IC tester.
The objective of the present invention is to solve the above problems, that is, to miniaturize an inspection apparatus of integrated circuits by decreasing the use of hardwiring such as optical fibers, and to improve precision in applying desired test signals to pins of integral circuits by preventing transmission losses and phase shifts (time shifts) of the signals.
To achieve the above objective, the apparatus for inspecting integrated circuits according to the present invention comprises:
a test signal generating device that outputs an optical test signal;
an optical distributor that distributes the optical test signal into a plurality of distributed optical signals by transmitting the optical test signal through a branching optical fiber network; and
a plurality of pin cards each of which generates an electric test signal by performing phase adjustment of each distributed optical signal;
wherein the pin cards are arranged so as to apply the electrical test signals to pins of an integrated circuit to be inspected.
According to the present invention, because the optical distributor distributes the optical test signal transmitted from the test signal generating device into a plurality of distributed optical signals, and the pin cards generate electric test signals by respectively performing phase adjustment of the distributed optical signals, it is possible to simplify the hardwiring between the test signal generating device and the pin cards, and the inspection apparatus can be miniaturized.
Furthermore, because an optical fiber can be used for the hardwiring between the test signal generating device and the optical distributor, it is not only possible to prevent cross talk of phase signals between pin cards, but also it is possible to reduce line noise, transmission loss, and deterioration in frequency characteristics.
The optical fiber network may comprise a plurality of optical fibers connected to each other via branch couplers to form a branching tree structure. For example, the branch coupler has a Y-shape.
The test signal generating device may further output phase control signals as well as the optical test signal, and each pin card may generate the electrical test signal having a phase delayed from that of the distributed optical signal by a time specified by each phase control signal. In this case, because the optical test signal is used as a master clock signal for phase adjustment of the electrical test signals, the accuracy in phases of the electrical test signals can be improved.
Only one optical fiber may be provided for transmitting the optical test signal to the optical distributor as a master clock signal which is a reference signal for the inspection.
The optical distributor may comprise a body having a cylindrical shape, and the branching optical fiber network may be fixed on the surface of the body so that output ends of the optical fiber network are arranged on an end of the body while forming a constant interval between neighboring output ends of the optical fiber network.
The optical distributor may have a cylindrical shape and be formed by bending a flexible plate on which the branching optical fiber network is fixed, and the branching optical fiber network may consist of a plurality of optical fibers connected to each other via branching couplers to form a tree structure.
The optical distributor may comprise a body having a disk portion and a plurality of protrusions standing up from the disk portion, and the branching optical fiber network may be fixed on the disk portion so that each of the output ends of the optical fiber network is fixed along each protrusion.
The optical distributor may have a disk shape and be formed by: providing the branching optical fiber network on a disk shaped plate so that terminal optical fibers of the optical fiber network are arranged radially toward the periphery of the plate; cutting the plate at both sides of the terminal optical fibers to form strip portions; and bending the strip portions so that they stand perpendicular to the disk shaped plate.
Each of the pin cards may comprise a light receiving element disposed facing each of the output ends of the optical fiber network for receiving each distributed optical signal.
The branching optical fiber network has a plurality of optical pathways extending from an input end to each output end thereof, and all the optical pathways have a constant length.
The branching optical fiber network consists of a plurality of optical fiber network units connected to each other in series.
An optical amplifier may be provided between the test signal generating device and the optical distributor for amplifying the optical test signal and applying amplified optical signals to the optical distributor.
Each of the pin cards may comprise a light receiving element, and the pin cards may be arranged spokewise around the optical distributor so that each light receiving element of each pin card faces each output end of the optical distributor.